Illuminated graphic keypads for automotive applications such as radios often have backlit insignia which identify the particular function of each button. Such backlit keypads employ a light source which is positioned behind the keypad in order to make the insignia visible in the dark, necessitating that the insignia be capable of receiving light from the light source. For this purpose, the keypad buttons are typically formed from a light conducting material, i.e., transparent and translucent materials.
A known process for manufacturing buttons and other backlit components is the use of paint and laser technology. These processes have generally involved forming the button from a transparent plastic material which may be painted white to form a white translucent layer over the transparent material, and then painted black to form an opaque black covering over the transparent material and, if present, the white translucent layer. The black covering is then lased away to form an insignia. The transparent nature of the button maximizes the transmission of light through the button for night time viewing. If present, the white translucent layer contributes graphics whiteness by reflecting light, such that the insignia is more readily visible under natural lighting conditions during daylight hours.
Paint and laser techniques of the type noted above have significant shortcomings. Insignias typically used in automobile graphic keypads have a stroke width (the line width of the insignia) of often less than one millimeter. Obtaining suitable optical characteristics with such intricate graphics requires controlling the thicknesses of the light conducting structures in order to maintain the desired lighting effect through the insignia. The ability to achieve a desired lighting effect is typically further complicated by the requirement for the backlit component to actuate an electrical switch beneath the keypad. Operation of the switch and efficient use of light sources often dictate that a light source cannot be located directly beneath a backlit component. Consequently, it can be difficult to achieve an adequate and uniform distribution of light to the backlit buttons of a keypad.
Even if uniform intensity is achieved within a single backlit component, differences in adjacent insignia often result in irregular illumination intensities within a backlit display group. This is particularly true with buttons of a backlit display which share one or more light sources. To minimize costs, such groupings often use a minimum number of light sources, and incorporate light pipes for the purpose of distributing the light energy equally to each of the backlit buttons.
Although much effort has been directed toward optimizing the design of light pipes, uniform backlighting of each and every backlit component is very difficult due to size and location restraints. As a result, facets and painted patterns have often been applied to light pipes in order to increase the light intensity directed to relatively dim areas. If additional lamps are used, excessively bright areas must be attenuated with printed halftone patterns behind the individual insignia. While such tactics have been effective for flat screen printed displays, it is costly and poorly suited for buttons and other backlit components which are not flat and have low lighting intensities.
Accordingly, it would be desirable to provide a backlit component whose structure is adapted to achieve a sufficient level of backlighting intensity by making efficient use of a minimal number of light sources.